Motion processing deficits in migraine are related to contrast sensitivity

Background: There are conflicting reports concerning the ability of people with migraine to detect and discriminate visual motion. Previous studies used different displays and none adequately assessed other parameters that could affect performance, such as those that could indicate precortical dysfunction. Methods: Motion-direction detection, discrimination and relative motion thresholds were compared from participants with and without migraine. Potentially relevant visual covariates were included (contrast sensitivity; acuity; stereopsis; visual discomfort, stress, triggers; dyslexia). Results: For each task, migraine participants were less accurate than a control group and had impaired contrast sensitivity, greater visual discomfort, visual stress and visual triggers. Only contrast sensitivity correlated with performance on each motion task; it also mediated performance. Conclusions: Impaired performance on certain motion tasks can be attributed to impaired contrast sensitivity early in the visual system rather than a deficit in cortical motion processing per se. There were, however, additional differences for global and relative motion thresholds embedded in noise, suggesting changes in extrastriate cortex in migraine. Tasks to study the effects of noise on performance at different levels of the visual system and across modalities are recommended. A battery of standard visual tests should be included in any future work on the visual system and migraine

Media Presence and Inner Presence: The Sense of Presence in Virtual Reality Technologies

Abstract. Presence is widely accepted as the key concept to be considered in any research involving human interaction with Virtual Reality (VR). Since its original description, the concept of presence has developed over the past decade to be considered by many researchers as the essence of any experience in a virtual environment. The VR generating systems comprise two main parts: a technological component and a psychological experience. The different relevance given to them produced two different but coexisting visions of presence: the rationalist and the psychological/ecological points of view. The rationalist point of view considers a VR system as a collection of specific machines with the necessity of the inclusion \ud of the concept of presence. The researchers agreeing with this approach describe the sense of presence as a function of the experience of a given medium (Media Presence). The main result of this approach is the definition of presence as the perceptual illusion of non-mediation produced by means of the disappearance of the medium from the conscious attention of the subject. At the other extreme, there \ud is the psychological or ecological perspective (Inner Presence). Specifically, this perspective considers presence as a neuropsychological phenomenon, evolved from the interplay of our biological and cultural inheritance, whose goal is the control of the human activity. \ud Given its key role and the rate at which new approaches to understanding and examining presence are appearing, this chapter draws together current research on presence to provide an up to date overview of the most widely accepted approaches to its understanding and measurement

A comparison of data mining and spatial techniques : an application to property data

The improvement of data management and data capturing techniques has led to the availability of large amounts of data for analysis. This is especially true in the field of spatial data, where data is indexed by location. Traditionally, spatially correlated data has been analysed using methods that rely on the spatial component of the data. This article will compare the results of using traditional spatial methods such as Kriging and geographically weighted regression against the use of other statistical data mining methods, given the large amount of data available. Using a dataset containing property values for the Tshwane Metropolitan area, different spatial and statistical models will be applied for predictive purposes in order to determine which model represents the data most accurately. Finally, these methods will be combined using stacking, to determine whether the combination of models has better predictive abilities than the single models.http://www.sastat.org.za/journal.htmam201

Estimation of linear detection mechanisms for stimuli of medium spatial frequency

Detection thresholds were obtained for a circularly-symmetric Gabor profile and Craik-Cornsweet profiles presented on a large white adapting field. These stimuli possessed peak spatial power between 1 and 6 c/deg. Their contrast was represented in an L, M and S cone contrast space. Detection thresholds were obtained for many vectors close to specific but theoretically important planes within this space. These data were fitted with a model comprising independent mechanisms, each a weighted sum of cone contrasts. The fit revealed a chromatic mechanism driven by ΔL/L - ΔM/M with no S cone input. Within cone contrast space, this mechanism was more sensitive than both a luminance mechanism with little S cone input but considerable variation in relative L to M cone input, and a blue-yellow chromatic mechanism

Influência da estrutura do catalisador a base de Zirconoceno na estereorregularidade e propriedades do polipropileno formado Influence of Zirconocene structure on polypropylene stereorregularity and properties

RESUMO: Catalisadores de metalocenos com diferentes simetrias, cocatalisados por metilaluminoxanas (MAO), foram avaliados em diferentes temperaturas de polimerização do propileno. Os metalocenos com ponte interanelar, ou seja, o dicloreto de rac-etileno bis(h5-1-indenil) zircônio, com simetria C2, e o dicloreto de isopropilideno(h5-ciclopentadienil)(h5-9-fluorenil) zircônio, com simetria Cs, produziram, respectivamente, polipropileno isotático e sindiotático. O grau de taticidade desses polímeros diminui com o aumento da temperatura de polimerização. Os metalocenos sem ponte, dicloreto de bis(h5-ciclopentadienil)zircônio e bis(h5-indenil)zircônio, em qualquer uma das temperaturas investigadas, produziram, somente, polipropileno atático. A estereorregularidade dos polímeros foram determinadas por Ressonância Magnética Nuclear de 13C.<br>ABSTRACT: Metallocenes with different symmetries in combination with methylaluminoxane (MAO), have been investigated at different propylene polymerization temperatures. The metallocenes rac-ethylene bis(h5-1-indenyl) zirconium dichloride, with C2 symmetry and isopropylidene (h5cyclopentadienyl)(h5-9-fluorenyl) zirconium dichloride, with Cs symmetry, produce isotactic and syndiotactic polypropylene respectively. The degree of tacticity of these polymers decreases with the increase of polymerization temperature. Only atactic polypropylene was formed with the unbridged zirconocenes bis(h5-cyclopentadienyl) zirconium dichloride and bis(h5-indenyl) zirconium dichloride at any temperature investigated. The polymer microtacticity was analysed by 13C NMR